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Term 2! > BIOL 273 - Unit 3.3 > Flashcards

BIOL 273 - Unit 3.3 Flashcards

1
Q

What happens to A band during muscle contraction

A

remains constant - therefore myosin shortening could not be responsible for muscle contraction

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2
Q

Describe the sliding filament theory

A
  • At rest the ends of thick (myosin) and thin (actin) filaments overlap slightly within each sarcomere
  • Thick and thin filaments slide past each other with no change in the length of the filaments themselves
  • The thin (actin) filaments slide along the thick (myosin) filaments towards the M line of the sarcomere - brings the Z disks closer together
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3
Q

What happens to the H zone during the sliding filament theory

A

decreases

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4
Q

What happens to the A band during sliding filament theory

A

remains constant

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5
Q

What happens to the Z discs during the sliding filament theory

A

closer to M line

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6
Q

What happens to the I band during the sliding filament theory

A

decrease

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7
Q

What do skeletal muscles need to be stimulated by to contract

A

somatic motor neuron from the nervous system

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8
Q

What is released by the neuron into the synaptic cleft at the neuromuscular junction, what does this neurotransmitter bind to?

A
  • ACh released
  • binds to nicotinic cholinergic receptors on highly folded muscle motor end plates (aka Na+/K+ channels)
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9
Q

What happens when ACh binds to Na+/K+ channels

A
  • allows Na+ and K+ to move across the membrane
  • ACh is removed by acetylcholinesterase
  • Na+ influx exceeds K+ efflux
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10
Q

What happens when Na+ influx exeeds K+ efflux , what is it called

A

local depolarization occurs at the synapse
- called End Plate Potential - EPP

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11
Q

What happens during depolarization , EPP, what structure does it interact with

A

the potential moves down the T-tubule system
- T tubule membrane contains dihydropyridine (DHP receptors) - L type calcium channel

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12
Q

What happens on the T-tubule membrane when it is depolarized

A
  • DHP receptors changes conformation
  • they are mechanically linked to Ca 2+ channels of the SR called ryanodine receptors (RyR)
  • RyR changes conformation whih allows for opening of SR Ca+2 channels (calcium leaves the SR)
  • increasing cytosolic Ca2+
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13
Q

What happens when calcium is roaming free in the cytosol

A

Ca+2 binds to troponin on the thin filament
- this moves tropomyosin into the “on” position revealing actin binding sites

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14
Q

the binding of calcium and acting on regulatory proteins on thin filament results in what process

A

the crossbridge cycle

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15
Q

What is myosin’s function in the crossbridge theory

A

converting chemical energy (ATP) into movement

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16
Q

What are the binding sites of myosin

A

actin and ATP

17
Q

When does myosin bind to actin during the crossbridge cycle

A

when actin is exposed when Ca2+ binds to troponin
- this forms the crossbridge

18
Q

What happens when the myosin heads binds to actin during crossbridge cycle , what is this process called

A

inorganic phosphate releases from myosin (1st)
- causes myosin head to pivot toward the centre of the sarcomere
- called the powerstroke
- pulls thin filament towards the M line
- followed by the released of ADP from myosin (2nd)

19
Q

When does the myosin head (crossbridge) detach

A

when a new molecule of ATP attaches to the myosin head

20
Q

When does the myosin head return to the cocked position

A

when the myosin head ATPase hydrolyses ATP to ADP and Pi

21
Q

When does relaxation of the skeletal muscle occur

A

When Ca2+ is pumped back into SR through the Ca2+ ATPase (against concentration gradient)
- decrease in calcium in cytosol causes troponin and calcium to unbind

  • troponin shift to too position and covers binding site on actin of thin filament
22
Q

When does Glycolysis occur , what does it produce

A

in the presence or absence of oxygen
- provides limited amount of ATP - 2
- produces lactic acid

23
Q

Creatine phosphate

A

high energy phosphate molecule
- highly concentrated in muscles , provides a rapid source of energy
- easily donates inorganic phosphate to ADP to create ATP (provides a limited supply of ATP)

24
Q

Purpose of creatine phosphate

A

buffer concenration of ATP over very short time
creatine + ADP to ATP + creatine
(catalyzed by creatine kinase)

25
Q

Twitch in muscle contraction

A

a single contraction-relaxation cycle
(dependant on the movement of calcium to and from SR)

26
Q

Latent period in muscle contraction

A

short delay between the AP and the beginning of the muscle tension

excitation and contraction coupling <- the time it takes for that to occur
- ends when calcium is binded to troponin to develop tension

27
Q

What are the three types of muscle fibres

A
  1. Slow-twitch fibres (type I)
  2. Fast-twitch oxidative-glycolytic fibres (type IIA)
  3. Fast-twitch glycolytic fibres (type IIX)

depends on the primary source of energy (glycolysis or oxidation)

28
Q

Oxidative fibres

A
  • dark red in appearance due to myoglobin
  • Myoglobin -> an oxygen carrying haeme protein
  • predominantly produce ATP via oxidative metabolism
  • diamater of cell is smaller , numerous mitochondria , many capillaries (vascularized)
29
Q

Fast or slow fibres

A
  • refers to the rate of myosin hydrolize ATP and undergo crossbridge cycle

Fast fibres: split ATP more quickly / crossbridge cycle & tension faster
- result of the presence of different isoforms of myosin

30
Q

Short twitch duration is useful for what

A

rapid, small muscle contractions (playing the piano)

31
Q

Long twitch duration is good for what

A

long sustained movements (lifting heavy loads)

32
Q

Twitch duration is determined by what

A

by the rate of removal of calcium ions from the cytosol

33
Q

Which muscle has highest rate of removal from cytosol

A

fast twitch muscles - includes the contraction AND relaxation

Term 2! (59 decks)

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